


Sin.  Sinner.  Sineater.

by Roar_Ra



Series: Sin [1]
Category: Supernatural
Genre: Boy King of Hell Sam Winchester, Fix-It, Hurt!Sam, Hurt/Comfort, M/M, Mark of Cain, Misunderstandings, Post-Episode: s10e14 The Executioner's Song, jealous!Dean
Language: English
Status: Completed
Published: 2015-05-15
Updated: 2015-05-15
Packaged: 2018-03-30 17:21:10
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 3,092
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/3945244
Author URL: https://archiveofourown.org/users/Roar_Ra/pseuds/Roar_Ra
Summary: <blockquote class="userstuff">
              <p>Sam and Castiel are hiding something.  The mark is getting worse.  Not all is as it seems.  Set post ‘Executioners Song’</p>
            </blockquote>





	Sin.  Sinner.  Sineater.

The mark burns; roaring and hissing, vile, evil whispers… demanding to be sated.

Dean closes his eyes, trying to banish the demonic hatred bubbling thru his blood, demanding satisfaction.

His chest aches in despair.

 

The worst part is THEM, the two of them.

Sam hovering; orbiting like a satellite. It's driving him insane.

Dean doesn't want him around, feels the ache more acutely when Sam is there. The mark wants death, no question, but it wants one particular death, lusts for the gush of his baby brother’s blood against it’s jagged teeth… and the hunger grows stronger each day.

Castiel is little better, throwing concerned glances Dean's way. Worry, and strangely anger seem to press onto the angel's features more deeply each day.

Dean begins to lose time, he's sure it's a side effect of the mark. 

Castiel begins spending more time with Sam, throwing anxious glances his little brother’s way. Dean catches the looks, the gestures of comfort they think he doesn't notice.

(sound of flesh meeting flesh, a shuddering moan from his brother's mouth… Dean rears back in horror as Castiel holds Sam possessively… 

"Forget." The angel whispers. And he does.)

__

 

The mark burns.

Sam finally starts showing some signs of higher brain function and stops hovering over Dean, often hiding in his room or disappearing for days on end.

He's relieved and furious at the same time.

They’re conspiring - he knows it in his bones, he just doesn't know why. Shouldn't Dean be a part of team 'get rid of the fucking mark'? It hurts, and this bitterness makes the mark burn hotter, twisting into something sour and sharp.

(Dean rounds the corner into Sam's room.

Sam and Castiel on the bed. The angel is caressing Sam, and worse Sam is leaning his head into the angels palm, eyes closed in bliss at the touch.

Rage and jealousy war for dominance. How dare Cas touch his brother. Sam is Dean's, no one else's. His to hurt, his to own, just HIS.

He leaps forward with a roar.

"Forget" The angel whispers. And he does.)

 

___

 

Dean tries the macho, shit eating grin, wisecracking, everything's fine act.

He isn't convincing anyone, least of all himself.

He's furious with Castiel - the mark wants him gone - the mark wants Cas out of the way so Dean and the blade can spend some quality alone time with what the mark of Cain really wants.

Sammy.

The mark screams for his brothers’ blood almost nonstop now. It's just a matter of time before Dean will have to make the choice. Dean will end it, or ask Castiel to. Asking Cas is the better option, but Dean's just to prideful and pissed off -why? He has no idea, something tickling at the back of his memories…- at the angel to ask.

 

____

Neither Sam nor Castiel notice him as Dean makes his way silently down the hall.

"I can't do this." Sam's voice is rough, a low tortured moan. "Dean will never forgive me…"

Dean could swear he almost hears remorse in Cas's low velvet purr. "You're right. He probably won't, but you won't stop, will you?"

"No, I won’t.” Voice so rough with need it’s nearly a sob. "I want this, I want it so badly… God help me, Cas-"

Shock numbed legs lead him back down the hall.

The angel isn't there to whisper "Forget." this time. So he doesn't.

___

 

He ignores them both for a week. 

He still loses time. Finds himself waking to Castiel holding his blood stained hands looking like he wants to cry. Or to Sam holding his head in his lap. Those are the worst. Signs that they still care.

___

 

The levee breaks the next week.

He loves them both, despite their betrayal. Dean knows the difference between the bloodlust of the mark and his own feelings. Dean knows for all his fuckups he'd never willingly want to kill his friend or his brother.

It turns out he was wrong.

Looking at the scene before him, Dean's mind refuses to comprehend it.

Sam naked. 

Sam at Castiel's feet. 

Lips locked around Cas’s wrist.

Blood.

Sam.

Blood.

Throat convulsing as Sam swallows-

Rage whites out everything. He must have made a noise, because Sam turns, blood dripping from that beautiful mouth.

Dean realizes this is it. He's going to kill them both. 

No blaming the mark, no excuses, it’ll be pure Dean Winchester. No turning back, no regrets.

Castiel holds up his had and Dean's frozen, eyes crazed with rage. 

The angel approaches and Dean bares his teeth like a dog.

A gentle touch to his forehead. "Remember."

And he does. All of it. Through their minds.

\-----

Sound of flesh meeting flesh, an unwilling groan from his Sam's mouth… Dean rears back in horror… 

Sam is on the floor, left eye already swelling.

"What the fuck, Dean?"

Dean looks down at his own hand in confusion. Sam hadn't done anything. Just laid a hand on his shoulder. And he'd… oh god. 

The horror must have shown on his face, because Sam is instantly contrite 

-contrite! As though he had any reason to be!-

"No! It's okay, Dean. It's okay. You didn't mean to do it."

-Stupid kid sounds like a battered housewife-

"Cas!" The panic in Dean's voice must carry because Castiel is there in a heartbeat.

The angel’s brow furrows, he is immediately on the floor holding the younger hunter, checking for injuries. 

Sam is trying to diffuse the situation.

"Hey, no problem. Cas, you can take care of this for me right? Just erase the last few minutes, heal me up and we'll get back to the books." 

The pleading panic in the taller man’s eyes must have convinced Castiel; because before Dean can come up with a dozen reasons this is a TERRIBLE idea… 

Castiel touches Dean’s forehead and whispers "Forget." So he does.

___

 

Sam doesn't allow the tears of pain to fall. Dean broke his arm this time and shattered his cheekbone.

He limps off to his room and waits for Cas. The healing takes time. Cas's grace doesn't have the mojo it once did, and he's expending too much, too quickly trying to keep Dean from realizing how far down the path the mark has taken him.

Dean can't know, not yet. Not before they have a solution. They'll loose him to suicide or madness. Neither of those is acceptable.

Castiel sits beside him and traces his fingers along the broken jawbone. Sam gasps as he feels the flesh and bone knitting back into place, sweet cool relief replacing the hot sear of pain, the younger man leans into the touch.

Dean rounds the corner and charges.

Castiel rolls his eyes and knocks him out cold. Familiar words leaving his lips. 

Sam hopes Dean isn't going to suffer brain damage from being mind wiped by an angel twice in one day.

 

___

 

Cas found it. The cure – no, not a cure. There is not cure. 

But there might be an… alternative solution.

Sam stares at Cas in shock. He rereads the ritual shaking his head in disbelief. Wants to deny it. Want's to deny how much he wants this… Want’s his brother; his soul mate to be bound to Sam forever. But Dean… he can't possible want… agree....

"I can't do this." Sam's voice is rough, a low tortured moan. "Dean will never forgive me…"

Dean could swear he almost hears remorse in Cas's low velvet purr. "You're right. He probably won't, but you won't stop, will you?"

"No, I won’t.” Voice so rough with need it’s nearly a sob. "I want this, I want it so badly… God help me, Cas-"

"I know this will be a heavy burden on you, Sam, but it's the only way."

The only way, how many times have they heard that now?

"He may not forgive you for taking the crown. But Dean will never forgive himself if he kills you."

Sam looks down at the parchment.

He’ll have to accept the crown of the boy king, binding Dean to him as his Knight, binding himself to Dean and Cas forever. 

A prince in name only, commanding an army of two, no longer required to lead hell’s legion, since Lucifer is still safely in the cage and NOT in Sam.

By accepting the crown, the title will allow him some leeway with regards to the mark. By making Dean his knight, Sam won’t be able to remove the mark, but will be possible to warp it, to change the sin.

The mark will continue to fixate on Dean's younger brother - but exchanging one sin for another.

Lust instead of killing. Incest instead of murder.

Dean will still be the sinner. Sam will be the sin.

"And you, Cas, what will this do to you?"

The angel looks down at the floor. "I'll become what's known as a sin-eater." If Sam didn't know better he'd think the smaller man was embarrassed. "I'll lose my ability to return to heaven, but gain my powers back in a more… um… carnal fashion."

Sam is afraid to ask.

"Every time you and Dean… feed… the mark, it will replenish my, um, fallen grace." Castiel suddenly finds the wallpaper fascinating. "So… given your feelings and Dean’s, I assume I'll gain a great deal of strength."

"Dean doesn't-"

Cas glares at Sam sharply. "Do not presume to understand your brother's love as completely as you think you do." Cas sounds annoyed that he even has to be explaining this. "His love for you is every bit as overwhelming, twisted, tormented, co-dependent and complex as yours is for him."

-can't be right-sammy doesn't love him like that-

Denial is clearly written across Sam's features. "I think your wrong Cas… Besides, I’m more than willing to give up heaven and hell for Dean, but we can't possible as you to sacrifice… to… to FALL for us."

Cas smiles, and Dean is shamed to see the selfless love reflected in the angel’s eyes. "Team free will, Sam. You would not ask. And Dean would never ask you to give up heaven for him."

-Wait, what???-

"I'm not giving up anything. It's not heaven if Dean's not there." Sam's eyes shine with unshed tears. "He's my soulmate." He smiles and it's the most beautiful thing Dean's ever seen. "If he wants me… If you want us. Team freewill gets to flip the bird to both heaven and hell. Stay right here fighting, for the next millennia or so."

-Sounds good, little brother-

Castiel hesitates almost imperceptivity. "Sam. This ritual will require some time, and, what I think you commonly refer to as an ass-ton of psychic energy. More than any human would be able to harness with the exception of you."

"Demon blood?”

Dean suddenly wants to gank the angel again.

"No. Not Demon. Sin eater. Or soon to be sin eater if all goes well."

Sam nods. "But no tricking him. Dean needs to know everything before he makes a choice." There still a sliver of bitterness there.

-sorrysammysorrysammy-

"We'll start the ritual now. Dean will feel the pull to you immediately when his part is ready. I apologize for any modesty issues you may have, but the ritual is… unsurprisingly… um… physical." 

Sam begins to shed his clothes and Cas turns away.

Dean has no such compunctions, watching the beautiful expanses of flesh as they are exposed.

“When it’s time, I will restore his memories and let him make his choice.”

____

 

Thrown back into his own body, Dean reels as he refocuses on the scene before him.

His brother, his beautiful overgrown, over muscled, baby brother. Naked before him, exposed completely, acres of skin marred only by scars (Dean knows every one and their story by heart) and sigils painted in blood. 

Hazel fox eyes look up at him, pleading for understanding. Pleading for acceptance. Pleading for love.

Forever, Sammy. You're it for me, you idiot. How could you ever doubt? Forever.

Bloodstained lips smile and Dean knows the answer is written on his face as clearly as Sam's own pleading. He undresses without being asked, unwilling to be ashamed at his own arousal.

Castiel beams at them both, as he places something that initially looks like a wreath on Sam’s head, but as it hits Sam’s skin, the plants shrivel, turning brown and wicked looking, leaves fall and long thorns begin to emerge.

How fitting, a crown of thorns for his own personal antichrist; a few spots of blood appear when they dig into the tender skin, but Sam’s expression is one of ecstasy more than agony. Cas smears the blood from Sam’s brow and transfers it onto Dean's arm, covering the mark. It burns. 

Sam crawls over to him and places his lips over Dean's forearm, sucking and licking over the mark. Claiming his knight.

The mark twists, fighting to keep it's anger, it's hatred. It tears thru Dean like a firestorm.

He drops to his knees mouth opening to scream - but it's covered by Sam's lips, the crush of Sam's body anchoring him. Dean can barely make out the high enochian chant behind them over the roar of desire, blood rushing everywhere, needing, desperate. 

Naked flesh slides against flesh. Yes, more need it all, everything. Always everything for Sammy. 

Castiel pricks his thumb with the blade, smearing it across Sam’s forehead, then Deans, then his own, a dark bloody version of an ash Wednesday ritual. 

Behind the kneeling brothers, soft shadow black feathers begin to fall from the angel’s wings, surrounding them and circling as electric-charged winds of energy swirl and howl.

Sam thrusts against him, hard cock sliding against his, flesh meeting flesh. Dean hisses in pleasure and wraps his hand around them both, already wet and messy with precome, his hand works easily down their shafts. Sam’s back arches at the sensation and Dean smiles with dark pleasure at his brother. So quickly, so close, it could be magic, or just their particular brand of it. Sensations start short circuiting Dean's brain. So close, just this. He feels his brother's orgasm through the psychic link before his own, redoubling his body's own pleasure.

Fuck the angels and demons, god and Lucifer, this is all he needs, his family.

The pleasure doesn’t stop, only redoubling in a way that shouldn’t be physically possible.

Behind Sam, Cas reaches out and places one hand on Dean's shoulder, while the other covers the mark. 

Sam's back bows sharply and his head snaps back, mouth open, a tendril of dark grace, black and glowing, leaving the newly crowned dark prince’s lips and entering the angel’s. Cas makes a choked sound, and they can feel thru the psychic bond the surge of lust and power that nearly brings Cas to his knees. 

It's like being caught in an electrical loop. Sam desire, want, lust, love, need, possession. And Cas, taking every bit of energy, loving it and feeding from it. 

The air above them explodes.

The brothers are thrown to the ground, Sam sags bonelessly into Dean's arms. Both men look up at their angel…

No, not their angel.

Their sin eater.

The last of Cas’s soft black feathers falling to the ground. 

Dean wants to weep for the loss and feels (god he can FEEL Sam in his head now) Sam's despair at the sight as well.

Castiel smiles, a little sadly, but then, somehow, flexes something, some set of muscles that are unseen. His wings snap open at full attention, high and huge. 

Cas is radiating dark power, he feels… he smells like sin and desire. 

The feathers have fallen away to reveal something sharper, slicker and much more powerful… They look like the wings of a-

"Dragon?" Sam’s half whisper is on top of Dean’s as his breathes the word “Awesome.”

Cas actually blushes in and looks down in an ‘aw shucks’ way. An innocent sin-eater, only Cas can manage to make that work. "Closer to an incubus than dragon actually… I have no particular interest in virgins."

-Well thank god for small favors-

Sam touches Dean's arm hesitantly, and Dean looks down at it in shock. The mark is no longer the ugly scythe shape. The pattern is still primal, tribal, branded into his flesh, but now in the shape of a triangle.

Their new trifecta.

Sam; the sin, the newly crowned boy king.

Dean; the sinner, knight of the boy king.

Castiel; their sin-eater, feeding from the power of a bond not recognized or understood by heaven or hell, but feared by both. 

Their guardian anti-angel.

Team free will.

The mark burns; demanding to be sated.

Dean's chest aches… with joy.

-

Epilogue:

Sam licks Dean’s hipbones, sucking the blood away from the two small wounds. “I’m so, so sorry, Dude… I didn’t…”

Dean laughs, “Hey, neither of us noticed them at first under all that girly hair. Who knew you’d get freaking HORNS out of this deal. We’ll just have to learn how to avoid that next time you go down on me… might take quite a bit of practice.”

Castiel hides a smile by pretending to examine his new wings.

Dean suddenly frowns, “Hey, Cas got a wing upgrade, you got horns – why didn’t I get anything?”

“What did you want – a tail or something?”

Dean considers Sam’s sarcastic quip for a moment, then nods and turns to Cas. “Yes, I want a tail, something at least 6 feet long and-.”

“Cas, don’t listen to him, Dean watches entirely too much tentacle porn, he’ll just use it to-“

Dean cuts his brother with a kiss and proceeds to send both he and Cas a very vivid image of holding Sam’s wrists above his head, tied by his (very long and sexy) tail. Sam is pressed between the two while Dean works his way down the front of his brother’s torso and Cas moans in pleasure while biting down of the neck of writhing man between them.

Sam’s mouth goes dry with want, he can’t seem to form words but manages a nod. Cas’s voice seems to drop even more as he whispers. “A tail… Okay, let me see what I can find about that.”

Dean laughs as he saunters towards the showers, leaving the two wrecked men in his wake. “And pie, let’s get some pie up in here, I’m starving.”

Cas and Dean give a small nod and smile in victory. It’s just another day in the bunker when Dean wants tail and pie.

**Author's Note:**

> AN – okay this was supposed to be all serious and angsty, then I had to go and make a sugar-crack epilogue and add a tail and pie joke… there is something seriously wrong with the author – sorry/not sorry!
> 
> This was originally a VERY short story about Dean getting the wrong idea when Cas is constantly needing to touch Sam in order to heal him after Dean hurts him, however it went completely sideways and turned into more of a sam/dean/cas vibe immortals and magic vibe.
> 
> I am currently working on a smutty sequel and threesome’y goodness to get me through the summer and soothe some of the emotional damage I’m sure the season 10 finale will inflict.


End file.
